Metallocene based catalyst systems which have been developed recently allow unprecedented control on polyolefin structures through catalyst design and have enabled the synthesis of entirely new families of homo and copolymers. Olefin polymerization catalysts comprising a metallocene and aluminum alkyl component are well known in the prior art. The molecular weight of the polymer product can be controlled by adjusting the reaction temperature or the amount of cocatalyst or by the addition of hydrogen. These catalysts require use of aluminoxane or cocatalyst, which is produced by reacting an aluminum alkyl with water. Such reaction is very rapid and highly exothermic. Processes for the production of olefins are known with the help of a homogeneous catalyst system consisting of a transition metal component metallocene, and a cocatalyst component of an oligomeric aluminum compound o aluminoxane (usually methylaluminoxane, herein after referred to as MAO), which lead to the higher activity with narrow molecular weight distribution polymers or copolymers.
Furthermore, U.S. Pat. No. 4,659,685, discloses polymerization of olefins with the aid of a solid catalyst comprising a zirconium based metallocene and a cocatalyst consisting of an organoaluminum compound, especially, MAO. However, this catalyst is preferably used in an aromatic hydrocarbon. It is not suited to heterogeneous processes of polymerization in suspension or in a gaseous phase.
The principle disadvantages of these soluble homogeneous metallocene-MAO catalyst systems are the need for a large excess of MAO, (Al/Metal&gt;10.sup.5) for obtaining reasonable polymerization activities, and poor control of polymer morphologies. Furthermore, when used in e.g. a gas or slurry process, there is a tendency for reactor fouling by forming deposits of the polymer on the surface or the walls of the reactor and stirrer. These deposits result in the agglomeration of the polymer particles when the metallocene and aluminoxanes or both, exist in the suspension medium. Such deposits in the reactor system must be removed regularly. Otherwise they prevent adequate heat removal from the reaction, adversely affecting the product quality.
The above disadvantages can be obviated by the use of heterogeneous catalysts, suitable for suspension polymerization in an aliphatic and aromatic hydrocarbon medium, and also in gas phase polymerization processes in which it is important to control the size, particle size distribution, and the morphology of the catalyst particle at the same time. Nevertheless, the catalyst should withstand the growth stresses during the course of gas-phase polymerization. It is also desirable that the solid catalyst be capable of producing an ethylene or an ethylene copolymer with an easily controllable average molecular weight and a narrow molecular weight distribution, which is a useful material for injection moulding.